1. Field of the Invention
The present invention relates to cam grinding machines for grinding a cam shaft and, more particularly, to a cam grinding machine provided with a pair of chucks for supporting journal portions at opposite ends of the cam shaft.
2. Description of the Prior Art
In a conventional method of grinding a cam shaft, center bores are first machined on opposite ends of the cam shaft. Journal portions of the cam shaft are then machined by a cutting tool and subsequently ground by a grinding wheel by using the center bores as a reference. Thereafter, as shown in FIG. 1, the cam shaft is supported by center members 3 and 4 of a headstock 1 and a tailstock 2 in a cam grinding machine, and a key member 5 is engaged with a key way formed on the cam shaft, whereby cam portions C of the cam shaft are ground in accordance with the profiles of master cams.
However, when journal portions are ground with some deviation relative to the center bores in the preceding machining step, the cam portions are also ground with some deviation relative to the journal portions because of the use of the center bores as a reference. Furthermore, the cam portions may be ground with some angular phase error relative to one another because of the existence of a backlash between the key member and the key way.
In order to reduce the number of machining processes which had been performed in the conventional method of finishing the cam shaft, it has been considered to grind unfinished journal portions in a rough grinding operation and a subsequent fine grinding operation by a centerless grinding machine without using a cutting tool and a center support. However, even if this method can reduce the machining processes for finishing the journal portions, it is impossible to thereafter finish the cam portions by the cam grinding machine using the center support.